This invention is generally directed to hydroxygallium phthalocyanines and photoconductive-imaging members thereof, and, more specifically, the present invention is directed to polystyrene/poly(methacrylic acid) diblock copolymers that can be selected as dispersant/binder polymers for photogenerating pigments, and more specifically, wherein the aforementioned diblock copolymers can be selected as resin binders for hydroxygallium phthalocyanines, especially Type V hydroxygallium phthalocyanine. The novel diblock copolymers of the present invention are comprised, for example, of an A block that binds to and is anchored to the photogenerating pigment surface, and a B block that functions primarily as a steric stabilizer to prevent, or minimize reflocculation of the photogenerating pigment after dispersion thereof. Examples of A blocks include polysulfonic acids, polyphosphonic acids, polycarboxylic acids, polyphenols, and the like; and B block examples include those blocks that are soluble in the organic solvent selected for preparation of the imaging member, such as polystyrene, poly(styrene-co-butadiene), poly(alkylstyrene), poly(alkyl acrylates), poly(alkyl methacrylates) and copolymers thereof.
To effectively permit coating of the photogenerating layer or binder generator layer (BGL) on the supporting substrate, it is usually necessary to dissolve the polymeric binder in a solvent suitable for coating, and disperse the photogenerator pigment in the solvent/binder mixture. Submicron size pigment particles are desired which often requires extensive grinding of the mixture in a ball mill or attritor. Large pigment particles, due to inefficient grinding or reflocculation, are considered undesirable for most purposes since they result in coating defects which subsequently surface as print defects. Therefore, it is of importance that the dispersion once formed remain stable for a minimum of about 7 to about 14 days to allow completion of the coating. For example, dip coating would require the dispersion to remain stable for a period of months, for example up to seven months. When HOGaPc is dispersed in commercially available binder resins, such as polyvinylbutyral, some settling or flocculation is evident within about 24 hours.
The addition of certain A-B diblock copolymers to a pigment, prior to milling, can provide superior dispersion, reference H. L. Jakubauskas, Journal of Coatings Tech., Vol. 58, No. 736, pages 71 to 82, 1986. The A block acts as an anchor on the pigment surface, while the B block extends out from the surface to provide steric stabilization. However, these types of materials cannot usually be incorporated into the binder generator layer (BGL) without adversely affecting the sensitivity, dark decay and cyclic stability of the resulting photoreceptor device. The block copolymer dispersants of this invention enable excellent imaging member sensitivity, and cyclic stability when compared to control devices, such as photoconductive imaging members with a BMS.RTM. polyvinylbutyral binder, or the specific aforementioned diblocks of the prior art.
Advantages achievable with the imaging members of the present invention include excellent photogenerating pigment dispersion at time zero, stable dispersions over time, and excellent flow properties. The A-B block copolymer in embodiments is designed such that the length and composition of the A segment enables it to bind or anchor firmly to the photogenerating pigment surface, while the B segment functions as a steric stabilizer to prevent reflocculation of the photogenerating pigment after dispersion. More specifically, photogenerating hydroxygallium phthalocyanines, such as Type V (HOGaPc), dispersions generated with the A-B block copolymers of this invention are stable in excess of several months, for example in embodiments up to about 1 year. In addition, the block copolymers function both as the dispersant and the binder. Alternatively, the block copolymers of the present invention can be used in combination with a second compatible binder resin, such as a resin similar to the steric stabilizing block like polystyrene, and which binder resin is selected in an amount of from about 20 to about 80 weight percent.
In embodiments, the Type V hydroxygallium phthalocyanine photogenerating pigment can be prepared as illustrated in U.S. Pat. No. 5,482,811 the disclosure of which is totally incorporated herein by reference, and more specifically, by the formation of a precursor gallium phthalocyanine with, for example, an X-ray powder diffraction trace having peaks at Bragg angles of 7.6, 8.1, 9.7, 16.0, 18.4, 19.2, 19.9, 24.7, 25.7 and 26.2, and the highest peak at 8.1 degrees 2.THETA., prepared by the reaction of 1,3-diiminoisoindolene with gallium acetylacetonate in a suitable solvent, such as N-methylpyrrolidone, or halonaphthalene like 1-chloronaphthalene, quinoline, and the like; hydrolyzing the precursor by dissolving in a strong acid and then reprecipitating the resulting dissolved pigment in aqueous ammonia, thereby forming Type I hydroxygallium phthalocyanine; and admixing the Type I formed with a hydrophobic solvent of, for example, hexanes, including n-hexane and/or isomers thereof, heptane, cyclohexane, cyclopentane or esters, such as propylacetate, butylacetate, or ketones such as methyl isobutyl ketone, methyl isoamyl ketone, or toluene, and thereafter, azeotropically removing water therefrom. More specifically, in embodiments the Type V process comprises the formation of a precursor prepared by the reaction of 1 part gallium acetylacetonate with from about 1 part to about 10 parts and preferably about 4 parts of 1,3-diiminoisoindolene in a solvent, such as quinoline, chloronaphthalene, or N-methylpyrrolidone, in an amount of from about 10 parts to about 100 parts and preferably about 19 parts, for each part of gallium acetylacetonate that is used, to provide a pigment precursor gallium phthalocyanine, which is subsequently washed with a component, such as dimethylformamide to provide the precursor gallium phthalocyanine as determined by X-ray powder diffraction, with an X-ray powder diffraction trace having peaks at Bragg angles of 7.6, 8.1, 9.7, 16.0, 18.4, 19.2, 19.9, 24.7, 25.7, and 26.2, and the highest peak at 8.1 degrees 2.THETA.; dissolving 1 weight part of the resulting gallium phthalocyanine in concentrated, about 94 percent, sulfuric acid in an amount of from about 1 weight part to about 100 weight parts and in an embodiment about 5 weight parts, by stirring the pigment precursor gallium phthalocyanine in the acid for an effective period of time, from about 30 seconds to about 24 hours, and in an embodiment about 2 hours at a temperature of from about 0.degree. C. to about 75.degree. C., and preferably about 40.degree. C., in air or under an inert atmosphere, such as argon or nitrogen; adding the resulting mixture to a stirred organic solvent in a dropwise manner at a rate of about 0.5 milliliter per minute to about 10 milliliters per minute and in an embodiment about 1 milliliter per minute to a nonsolvent, which can be a mixture comprised of from about 1 volume part to about 10 volume parts and preferably about 4 volume parts of concentrated aqueous ammonia solution (14.8N) and from about 1 volume part to about 10 volume parts, and preferably about 7 volume parts of water, for each volume part of acid like sulfuric acid that was used, which solvent mixture was chilled to a temperature of from about -25.degree. C. to about 10.degree. C. and in an embodiment about -5.degree. C. while being stirred at a rate sufficient to create a vortex extending to the bottom of the flask containing the solvent mixture; isolating the resulting blue pigment by, for example, filtration; and washing the hydroxygallium phthalocyanine product obtained with deionized water by redispersing and filtering from portions of deionized water, which portions are from about 10 volume parts to about 400 volume parts and in an embodiment about 200 volume parts for each weight part of precursor pigment gallium phthalocyanine selected. In further embodiments, there can be selected as a reactant an alkyoxygallium phthalocyanine dimer, reference copending patent applications U.S. Ser. No. 233,834, U.S. Pat. Nos. 5,466,796 and 5,456,998, the disclosures of which are totally incorporated herein by reference. In U.S. Pat. No. 3,473,064, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of hydroxygallium phthalocyanine Type V, essentially free of chlorine, whereby a pigment precursor Type I chlorogallium phthalocyanine is prepared by reaction of gallium chloride in a solvent, such as N-methylpyrrolidone, present in an amount of from about 10 parts to about 100 parts, and preferably about 19 parts, with 1,3-diiminoisoindolene (DI3) in an amount of from about 1 part to about 10 parts, and preferably about 4 parts of DI3 for each part of gallium chloride that is reacted; hydrolyzing said pigment precursor chlorogallium phthalocyanine Type I by standard methods, for example acid pasting, whereby the pigment precursor is dissolved in concentrated sulfuric acid and then reprecipitated in a solvent, such as water, or a dilute ammonia solution, for example, from about 10 to about 15 percent; and subsequently treating the resulting hydrolyzed pigment hydroxygallium phthalocyanine Type I with a solvent, such as N,N-dimethylformamide, present in an amount of from about 1 volume part to about 50 volume parts and preferably about 15 volume parts, for each weight part of pigment hydroxygallium phthalocyanine that is used by, for example, ball milling said Type I hydroxygallium phthalocyanine pigment in the presence of spherical glass beads, approximately 1 millimeter to 5 millimeters in diameter, at room temperature, about 25.degree. C., for a period of from about 12 hours to about 1 week, and preferably about 24 hours such that there is obtained a hydroxygallium phthalocyanine Type V, ball milling contains very low levels of residual chlorine of from about 0.001 percent to about 0.1 percent, and in an embodiment about 0.03 percent of the weight of the Type V hydroxygallium pigment, as determined by elemental analysis.
The Type V hydroxygallium phthalocyanine can be selected as organic photogenerator pigments in layered photoresponsive imaging members with charge transport layers, especially hole transport layers containing hole transport molecules such as known tertiary aryl amines. The aforementioned photoresponsive, or photoconductive imaging members can be negatively charged when the photogenerating layer is situated between the hole transport layer and the substrate, or positively charged when the hole transport layer is situated between the photogenerating layer and the supporting substrate. The layered photoconductive imaging members can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein negatively charged or positively charged images are rendered visible using toner compositions of appropriate charge polarity. In general, the imaging members are sensitive in the wavelength region of from about 550 to about 900 nanometers, and in particular, from about 650 to about 850 nanometers, thus diode lasers can be selected as the light source.
In U.S. Pat. Nos. 5,384,223 and 5,384,222, the disclosures of which are totally incorporated herein by reference, there is illustrated a photoconductive imaging member comprised of a supporting substrate, a photogenerating layer comprised of photogenerating pigments dispersed in a polystyrene/polyvinyl pyridine (A.sub.n -B.sub.m) block copolymer wherein n represents the degree of polymerization of A, and m represents the degree of polymerization of B, and a charge transport layer, and wherein, for example, n is a number of from between about 7 to about 50, and A represents the anchoring block for said pigments, and B represents the block that functions primarily as a steric stabilizer; and wherein m is a number of from between about 70 to about 800; and a process for the preparation of a photogenerating composition which comprises mixing titanyl phthalocyanine Type IV, or BZP with the AB block copolymer polystyrene-b-poly(4-vinyl pyridine) in a suitable solvent. Examples of block copolymers disclosed in these copending applications include those wherein A is a basic anchoring group, such as poly(2-vinylpyridine), poly(4-vinylpyridine), poly[p-(dimethylamino methyl)styrene], or poly[ 2-(dimethylamino)ethyl methacrylate], and the B block is a polystyrenic, polydiene, or polymethacrylate, such as polystyrene/poly(4-vinylpyridine), with a molecular weight of from about 11,000 to about 35,000. In contrast to the preferred use of basic anchoring groups with BZP, we have found that use of an acidic anchoring group with HOGaPc provides exceptional stability of the copolymer/HOGaPc coating dispersion with respect to settling, with no reduction in sensitivity and excellent cycling behavior. Therefore, the binders of U.S. Pat. Nos. 5,384,223 and 5,384,222 are inferior in some respects for use with HOGaPc.
The disclosures of all of the aforementioned publications, laid open applications, copending applications and patents are totally incorporated herein by reference.